The present invention relates generally to systems for recording and reproducing information signals on and from recording mediums, and more particularly to a system for recording an information signal with high density and, moreover, for recording a reference signal for providing tracking control at specific positions on a recording medium and reproducing the same.
A laser beam is used in one example of a system for recording and reproducing an information signal with high density. A video signal and/or an audio signal are recorded on and reproduced from a recording medium. In this system, a laser beam is used to record and reproduce the information signal optically on and from a rotating recording medium. In the reproducing portion of this system, it is necessary to exercise tracking control so that the reproduction laser beam will accurately trace the track recorded on the rotating recording medium.
One known example of a system for accomplishing this tracking control uses a light beam obtained by dividing a light beam normally used for reproducing after it is reflected from the recording medium. The divided beam is used for tracking control. Another known tracking control system uses a reproducing light beam which is divided into one main light beam for reproducing and two subsidiary light beams for tracking. The tracking control is achieved by these subsidiary light beams.
All of these known tracking control systems, however, have required complicated and expensive apparatus, have produced unstable operation, and have been incapable of accomplishing positive and accurate tracking control.
Accordingly, a possible system for solving these problems accompanying known tracking control systems would appear to use a single laser beam system. The beam records a main information signal and is deflected at a specific part on the main information track. The deflected beam records a tracking signal on this specific part. In this system, however, at least the main information signal is disturbed or interrupted by the deflection. Consequently, a continuously reproduced signal of high quality cannot be obtained. Furthermore, means for compensating for the interrupted signal is necessary. The reproducing apparatus becomes complicated and expensive.
Another example of a system for recording and reproducing information signals is a system which records and reproduces an information signal as a variation of electrostatic capacitance or as a variation of mechanical vibration. A rotating recording medium reproduced by these systems has a spiral guide groove formed thereon, for guiding a tracing stylus used for reproducing a signal. Along the bottom part of this guide groove, there is formed a track of an information signal which is recorded as a variation of a geometrical configuration. The tracing stylus is guided by this guide groove while tracing the bottom thereof and thus reproduces the recorded information signal.
However, a recording and reproducing system of this known type has been accompanied by various problems as enumerated below.
(a) If a video signal is to be recorded as an information signal, the groove pitch on the recording medium unavoidably must be made less than a number of .mu.m, because the frequency band of a video signal is wide and is recorded with high density. As a consequence, the area of the contact with the recording medium and the shape of the tracing stylus are limited by the groove pitch dimension. For this reason, there is a large contacting force per unit area at the contacting parts between the tracing stylus and the recording medium. As a consequence, the serviceable life of the tracing stylus and of the groove on the recording medium are very short.
(b) The stylus jumps if the stylus pressure is reduced in order to suppress abrasive wear of the tracing stylus. The stylus pressing force has been reduced to a minute value of 30 mgr., for example, with a resultant jumping of the stylus.
(c) As the abrasive wear of the tracing stylus progresses, it becomes increasingly easy for the tracing stylus to vibrate within the guide groove. Under this condition, the reproducing operation becomes unstable. Furthermore, the wear of the tracing stylus is promoted. This vibration phenomenon is attributable to the sticking and slipping of the tracing stylus which occur within the guide groove at the time when the tracing stylus is being compulsorily guided by the guide groove.
(d) When the tracing stylus vibrates, a great pressure is applied locally in a concentrated manner on the side walls of the guide groove. The film on the groove side wall surface is scraped off. Particularly, severe scraping occurs at the outer peripheral part of a rotating recording medium where the relative velocity of the tracing stylus and the recording medium is large. It is observed that the scraping of the guide groove wall surfaces are converted into the state of fish scales.
(e) As another consequence of the above described abrasive scraping, fine pieces of scraped off film adhere to the tracing stylus and give rise to frequent interruptions or skipping and deterioration of the reproduced signal. As a result of observation and an analysis of the foreign matter adhering to the tracing stylus under these circumstances, it was discovered that the foreign matter comprised the dielectric material covering the recording disc surface and the underlying metal film material. In some cases, it was found that the foreign matter further contained polyvinyl chloride (PVC), which is the material of the recording disc. This finding verifies that the foreign matter deposited on the tracing stylus is not a substance which has infiltrated from the outside, but comprises almost entirely materials scraped off from the recording disc.
(f) If a tracing stylus is compulsorily guided by the guide groove, it is theoretically impossible to have special modes of reproduction such as still motion, slow-motion, intermittent frame-by-frame, high-speed searching for a reproduction start point, and information search, etc.
(g) The tracing stylus and the guide groove are very fine and intricate in shape, and therefore are difficult to make.
(h) Since the signal groove has been formed on the recording disc, the process of recording the information signal on the original disc is laborius and complicated.
Accordingly, in order to overcome the various above described problems which arise from the guide groove, the invention sets forth the recording of an information signal as a variation of a geometrical form on a rotating recording medium, without providing a guide groove.
However, since there is no groove for compulsorily guiding the tracing stylus, it is necessary to provide means for causing the tracing stylus to trace positively and accurately over the recorded track. Accordingly, the invention provides a tracking control of the tracing stylus so that it will trace accurately and positively over the recorded track. The invention has made it possible to record and reproduce signals in a system which does not have a guide groove, as described above.